After opening your calibration slide image in the ChromaCal Image Calibration software, achieve a Matrix Alignment = “Good” before relying on the Exposure result.
When the CHROMACAL slide image is exposed correctly, the brightest white circle should be slightly gray, and the two whitest circles should differ in intensity. A correctly-exposed image will appear dark and certain patches may not be visible. This is normal. IMPORTANT: To adjust the brightness of the CHROMAL slide image at your imaging workstation, modify exposure; do not change the illumination!
Examples of proper and incorrect exposure of the CHROMACAL slide are below.
Adjusting Exposure in your Camara Software:
If the diagnostic result within CHROMACAL is “overexposed”, this means the whitest circle is much too bright and has clipped at least one of the color channels. If you continue, the color calibration will likely not be optimal and the calibrated specimen images will likely be darker than your original images.
As general guidance to proper exposure, during image capture of the CHROMACAL calibration slide, adjust exposure on your camera until the brightest white circle in the matrix is slightly gray. When the calibration slide image is exposed correctly, the image will appear dark and certain patches may not be visible. This is normal.
You can determine the correct exposure in any of the following ways:
1. If you are using auto-exposure, allow the camera to set exposure but only if the calibration slide image appears dark and the brightest white circle appears slightly gray. If the image is over-brightened, turn off auto-exposure and set exposure manually according to (2), (3) or (4) below; or
2. Acquire the calibration slide image at the same exposure as you used for specimen images taken with a non-oil immersion, “dry” lens; or
3. Use a histogram in your camera software to be certain that the brightest part of the histogram display is within the dynamic range of the camera as you reduce or increase your exposure; or
4. Set by eye; reduce exposure until the brightest white circle becomes slightly gray.